Researchers have identified for the first time the mechanism by which chronic stress causes hair color loss, an advance that can lead to the development of new medications that can prevent hair from turning gray.
In the study, published in the magazine. NatureThe scientists induced intense pain in special black mice for several weeks using a substance called resiniferatoxin, and turned the fur of the animals completely white.
“For a long time it has been said that stress causes the hair to turn white, but until now there was no scientific basis for this belief. Our study showed that the phenomenon does occur and we identify the mechanisms involved,” said Thiago Mattar Cunha of Harvard University in the United States.
“In addition, we discovered a way to interrupt the process of hair color loss due to stress,” Cunha said.
The researchers said that resiniferatoxin, which activated sensory nerve fibers, is a natural chemical found in the resin spur (Euphorbia resinifera), a cactus-like plant native to Morocco.
According to scientists, the sympathetic nervous system, which triggers the rapid involuntary response of the body to dangerous situations, is directly affected by stress and consists of nerves that branch out from the spine and run throughout the body.
It controls the “fight or flight” response of the organism to the sudden danger, launching a sudden flood of the hormones adrenaline and cortisol so that the heart beats faster, the increase in blood pressure, accelerated breathing and pupils dilate, between other systemic effects, they added.
The researchers observed that when the sympathetic nervous system was blocked, hair whitening was slowed.
“After injecting resiniferatoxin into the mice, we treat them with guanetidine, an antihypertensive drug capable of inhibiting neurotransmission through sympathetic fibers. We observe that the process blocked the process of hair color loss,” said Cunha.
In another experiment, in which the researchers surgically removed the sympathetic fibers, the color of the coat was retained again in the weeks after the induction of pain.
“These and other experiments carried out by our group demonstrated the involvement of sympathetic innervation in acromotricia and confirmed that pain is a powerful stressor in this model. But the mechanisms involved were still to be detailed,” said Cunha.
Previous studies had found that pain-related stress was also involved in the development of hair and skin pigment producing cells called melanocytes.
Scientists had discovered that stem cells not specialized in the hair follicle bulb “mature” too soon under stress.
“In a young individual, the cells are not differentiated, like all stem cells, but with aging, they gradually differentiate. Once the process is complete, they stop producing melanocytes that produce melanin,” Cunha said.
“We use various methodologies to show that intense sympathetic activity significantly accelerates differentiation. In our model, therefore, pain accelerated the aging of melanocyte stem cells,” he added.
A few days after the study, the researchers found that all pigment regenerating stem cells were lost.
When the researchers compared the genetic activity of the mice that received the injection of resiniferatoxin, developing pain, stress and loss of fur color, with those of the mice injected with a placebo, they discovered that a gene that played a role in the production of the cell division was involved a protein called CDK (cyclin dependent kinase).
In a follow-up experiment, when researchers treated mice with a CDK inhibitor, they found that differentiation of melanocyte stem cells was avoided, along with the loss of coat color.
“This finding shows that CDK participates in the process and therefore could be a therapeutic goal,” said Cunha.
“It is too early to know if one day it will become a goal in clinical practice, but it is worth exploring more.”